Restricting Access to Key Fields
The Key Fields lists in the Details tab or in the Basic Information tab are visible only to the users or groups specified as having Read Access to the Key Fields lists. However, other users may still be able to access the fields in the list through the User-Defined Fields tab or through other Key Fields lists.
Assigning a field to a Key Fields list does not determine who can access the field. The field is available as a Key Field only to users with access to both the user-defined field and to the Key Fields list.